1. Field of the Invention
The present invention relates to a substrate having a silicon-on-insulator (SOI) structure obtained by slicing a semiconductor layer from a crystalline semiconductor substrate and bonding it to a substrate of a different kind. In particular, the present invention relates to bonding SOI technology. The present invention relates to a method for manufacturing an SOI substrate in which a single crystal or polycrystalline semiconductor layer is bonded to a substrate having an insulating surface of glass or the like. Further, the present invention relates to a semiconductor device using a substrate that has such an SOI structure and a method for manufacturing such a semiconductor device.
2. Description of the Related Art
Instead of silicon wafers that are manufactured by thinly cutting an ingot of a single crystal semiconductor, semiconductor substrates called silicon-on-insulator (SOI) substrates have been developed, which have a thin single crystal semiconductor layer over an insulating layer and are becoming widely used as substrates for manufacturing microprocessors or the like. This is because an integrated circuit using an SOI substrate draws attention as an integrated circuit in which parasitic capacitance between drains of transistors and a substrate can be reduced, performance of the semiconductor integrated circuit can be improved, and low power consumption can be achieved.
On the other hand, attempts to form an SOI layer on an insulating substrate of glass or the like have been made. An SOI substrate in which a thin single crystal silicon layer is formed over a glass substrate having a coating film, by a hydrogen ion implantation separation method is known as one example of an SOI substrate in which an SOI layer is formed over a glass substrate (see Reference 1: Japanese Published Patent Application No. H11-163363). Also in this case, the thin silicon layer (SOI layer) is formed over the glass substrate in such a way that a microbubble layer is formed at a predetermined depth from the surface by implanting hydrogen ions into a single crystal silicon flake, bonding the glass substrate and the single crystal silicon flake, and then separating the silicon flake using the microbubble layer as a cleavage plane.
Also in the case of forming an SOI layer over an insulating substrate, a single crystal silicon layer is separated from a silicon wafer; therefore, the area of the single crystal silicon layer would depend on the area of the silicon wafer.
For example, a large display is manufactured by bonding a single crystal silicon layer to a glass substrate, a silicon wafer of φ 300 mm is commonly used, and the size of the silicon wafer is smaller than the size of the glass substrate. Therefore, the entire surface of the glass substrate cannot be covered by one silicon wafer.
Therefore, although a plurality of silicon wafers are required to be bonded onto the glass substrate, it is difficult to closely spread a plurality of silicon wafers over the glass substrate.
There is no silicon in the space between adjacent silicon wafers, so that there are constraints on circuit design, which greatly reduces latitude in design rules.